Isoparaffin alkylation

ABSTRACT

A strong acid catalyzed alkylation process wherein an isoparaffin is alkylated with an alkylating agent such as olefin hydrocarbon, alkyl sulfates, in the liquid phase, at a superatmospheric pressure and a temperature in the range of from below zero to about 100*F., and wherein gaseous carbon dioxide is dissolved in the strong acid catalyst.

Unlted States Patent 1191 1111 3,867,475

Estes et al. Feb. 18-, 1975 [5 ISOPARAFFIN ALKYLATION 2,468,529 4/1949 Voorhies et a]. 260/683.59

2,520,391 8/1950 Findlay 260/683.59 [75] John Estes P B Falls 3,489,818 1/1970 Hcrvert 260/68351 g y Cole, Flshklll, both of 3,531,546 9/1970 Hervert.....p.' 260/683.51

[73] Assignee: Texaco Inc., New York, NY. Primary Examiner-Paul M- Coughlan,

Attorney, Agent, or Firm-Th0mas H. Whaley; C. G. [22] Flledz Mar. 21, 1973 Ries [21] Appl. No.: 343,322

[57] ABSTRACT 52 us. c1 260/683.63, 252/436, 260/683.58 A Strong acid catalyzed alkylation process wherein an 51 1111.01. C076 3/54 isoparaffin is alkylated with an alkylating agent Such [58] Field of Search..... 260/683.63, 683.51, 683.59; 88 Olefin hydrocarbon, alkyl sulfates, in the qu 252/436 phase, at a superatmospheric pressure and a temperature in the range of from below zero to about 100F., 5 References Qit d and wherein gaseous carbon dioxide is dissolved in the UNITED STATES PATENTS 2,286,184 6/1942 Bradley et al 260/683.63 5 Claims, N0 Drawings ISOPARAFFIN ALKYLATION BACKGROUND OF THE INVENTION The present invention relates to alkylation of isoparaffin hydrocarbons with olefins in the presence of a strong acid catalyst. Particularly, the invention relates to production of C C hydrocarbon suitable for use as motor fuel by alkylation of isoparaffin hydrocarbon with olefins. More particularly, this invention relates to an isobutane-butylene alkylation process catalyzed by sulfuric acid and/or flurosulfonic acid, having high selectivity for production of trimethyl pentanes.

Acid catalyzed alkylation wherein an-alkane is added to an alkene is well known. The alkylation reaction is generally carried out in the liquid phase at a temperature usually below about 100F.'and at a pressure sufficient to maintain reactants in the liquid phase. Of particular importance is alkylation of isobutane with butylene to form octane hydrocarbons, especially trimethyl pentanes, which are useful as components of motor fuel. The butylenes which may be a mixture of normal and isobutylenes are reacted with a molar excess of isobutane in the liquid phase in the presence of a strong acid such as sulfuric acid, flurosulfonic acid, and mixtures thereof, at a temperature of F. to 100F. and a pressure of 10 to 150 psig, or higher.

The discussion herein is presented with respect to formation of octane hydrocarbons, however, it is to be understood that the discussion is equally applicable to alkylation reactions generally, and particularly to alkylation of isobutane and isopentane with lower molecular weight olefms such as propylene. butylenes, and pentalenes. Basically, it is desirable in an alkylation reaction to promote formation of the 1:1 olefin-paraffin adduct. That is, formation of octane from butylenes and paraffins. In strong acid catalyzed alkylation reactions, side reactions occur in which C products are formed as well as the desirable 1:1 olefin-paraffin adduct. A portion of C products then undergo cracking to form undesirable lighter hydrocarbons, such as for example, C C and C light alkylate hydrocarbons. The result of such side reactions,then, is to reduce production of the desired C products and to lower the octane number of the alkylate product obtained.

SUMMARY OF THE INVENTION Now, according to the method of the present invention, an improved strong acid catalyzed alkylation processis disclosed wherein production of desirable 1:1 olefin-isoparaffin adduct is increased. In the method of the present invention, olefin hydrocarbon is reacted with a molar excess of isoparaffm hydrocarbon at a temperature of from about 0F. to about 100F., a pressure of about 10 psig to about 150 psig and higher, in the presence of a carbon dioxide treated strong acid catalyst such as sulfuric acid, flurosulfonic acid and mixtures thereof. In a preferred embodiment, the carbon dioxide treated strong acid catalyst is prepared by contacting liquid strong acid with carbon dioxide gas at a temperature in the range of 0F. to 75F.,' a pressure in the range of 50 psig to 1000 psig and under condilyst of the prior art is employed. Additionally, formation of undesirable, low octane number light alkylate and heavy alkylate hydrocarbons is decreased. In an alkylation process of the present invention, employing a carbon dioxide treated strong acid catalyst, wherein isobutane is alkylated with butylenes, octane hydrocarbons are the major product of the process. Also, the major portion of the octane hydrocarbon alkylate is comprised of trimethyl pentanes which have high octane numbers and are particularly desirable as components for gasoline blending. Reduction of light alkylate components and C; heavy alkylate components, by following the method of the present invention, improves volatility characteristics of the alkylate product.

These, and other advantages will be more fully set out 7 in the detailed description of the invention which follows.

DETAILED DESCRIPTION OF THE INVENTION Unexpectedly,according to the present invention, we have discovered that incorporation of carbon dioxide gas into liquid alkylation acid catalysts improves subsequent alkylation reactions by increasing the yield of desirable 1:1 isoparaffin-olefin adducts, particularly the desirable highly branched isomers. The reasons for such improvement are not presently known. It may be speculated that solution of carbon dioxide into the acid catalyst reduces the acid viscosity such that better mixing of hydrocarbon reactant and catalyst is obtained, or that hydrocarbon solubility in the acid catalyst is'increased. However, such speculations are unsupported and are not to be taken as limitations upon the present invention.

Carbon dioxide treatment according to the method of the present invention is applicable to strong Bronsted acid alkylation catalysts. The strong Bronsted acids are those which readily give up a proton, and include HF as well as H H SO SO H SO H- acids are the catalysts used in the (C to C isoparafinto the liquid catalyst. Preferably, liquid acid and gase-- ous carbon dioxide are contacted under conditions of intimate mixing at superatmospheric pressures and temperatures in the range of below zero to 100F. More perferably, pressures in the range of about 50 1000 psig tions of good mixing to dissolve carbon dioxide into the andtemperatures in the range of 2075F. are em .ployed. Higher pressures and lower temperatures favor solution of carbon dioxide in the liquid strong acid. Pressures of atmospheric and higher are effective, and pressures of at least 50 psig are preferred. Pressures greater than about 1000 psigdo not offer any substan-. tial economic advantage. Lower temperatures favor solution of carbon dioxide in liquid strong acid. At temperatures below about 20F., liquid viscosity increases substantially and extra refrigeration must be provided.

Temperatures in the range of about 20-60F. are

within the usual temperature range of the alkylation reactions contemplated herein, thus extra refrigeration to cool the liquid strong acid is not required. Benefits of the present invention are obtained by dissolving carbon dioxide into the liquid strong acid catalyst. Maximum benefits are obtained when the strong acid is saturated with carbon dioxide at the alkylation reaction conditions employed. In order to encourage solution of carbon dioxide in strong acid, it is usually desirable to employ an excess of carbon dioxide. In treating the strong acid, weight ratios of carbon dioxide to strong acid of about 0.1/100 and higher may be employed. Preferably weight ratios of carbon dioxide to strong acid of at least 5/100 are employed. Great excesses of carbon dioxide to strong acid in the acid treatment are not necessary,

and excess carbon dioxide which does not dissolve in treated strong acid may be recovered for treatment of additional acid.

Intimate mixing of carbon dioxide gas with liquid strong acid may be accomplished by any effective gasliquid contact means such as asperation, sparging, agitation, etc. In a preferred mode of operation, carbon dioxide and strong acid are contacted before employing the treated strong acid as catalyst in an alkylation reaction. In processes wherein alkylation acid is recycled from an acid settler to an alkylation reaction zone, the recycle acid may be conveniently treated with carbon dioxide in a separate treatingzone prior to introduction into the alkylation reaction zone. However, if desired, the carbondioxide may be introduced directly into the alkylation reaction zone with mixing means provided to ensure contact of acid catalyst with hydrocarbon reactants also being used to contact the acid catalyst with the carbon dioxide.

Contact time of carbon dioxide with strong acid being treated need only be sufficient for solution of the desired amount of carbon dioxideint'o the strong acid. Contact times of from a few seconds to 24 hours and longer may be employed. Necessary contact time will be shorter with better mixing and more intimate contact of carbon dioxide with the strong acid. Preferred contact times for any particular acid treating system may be easily established by observing the rate of solution of carbon dioxide into the strong acid under the conditions of pressure, temperature and degree of mixing present in the particular system under consideration.

Conventional strong acid catalyzed alkylation reactions may be carried out employing the improved process of the present invention. Thus, the alkylation can comprise reaction of an isoparaffln with an olefin or other alkylating agent. In sulfuric acid and flurosulfonic acid catlyzed alkylation reactions, alkylsulfates, such as diisopropylsulfate, diisobutylsulfate, dibutylsulfate, etc., may replace the corresponding olefin in whole or in part as alkylating agent.

The alkylation reactions contemplated in the present invention are carried out in the liquid phase. However, the reactants need not be normally liquid hydrocarbons. Alkylation reaction conditions can vary in temperature from below zero to about 100F., and can be carried out at pressures of from atmospheric to 1000 psig and higher. For continuous'processes, olefin space velocities of from about 0.01 to about volumes olefin/hour/volume of catalyst may be employed. Molar ratios of isoparaffin hydrocarbonto alkylati'ng agent of from about 1:1 to about 50:1 and higher may be emloyed. Preferably, substantial molar excess of isoparaffin to olefin is maintained in an alkylation reaction, with molar ratios of isoparaffin to olefin of'from about 5:1 to about 20:1 being particularly preferred.

Strong acid alkylation catalysts can be employed in the alkylation reactions. However, sulfuric acid and mixtures of sulfuric acid and flurosulfonic acid are preferred. 1n the process of the present invention,.where a carbon dioxide treated strong acid catalyst is employed, the preferred temperatures for use of sulfuric acid are between 30 and F. and preferred'pressures are 50 psig to 150 psig and higher. When using flurosulfonic acid as catalyst, preferred temperatures are betwen 0and 75F. and preferred pressures are 50 psig to 150 psig and higher.

The following examples are offered to illustrate the improvement of the present invention.

EXAMPLE I To demonstrate the present invention, 300 ml. of 94.43 weight percent sulfuric acid, containing'30 ml'. of acid from a previous alkylation run, was charged to a reactor equipped with cooling coils and a stirrer. The autoclave was pressured to psig with CO and the acid was stirred at about 50F. for 15 minutes. Upon .completion of the stirring, the autoclave was depressured to 50 psig and 77 grams of hydrocarbon comprising isobutane and butene-2 in a volume ratio of 6.25/1 was charged to the reactor. Under alkylation conditions including a temperature of 50F., a pressure of about psig and constant stirring, the acidhydrocarbon mixture was allowed to react for 15 min utes. At the end of the reaction time the stirring was stopped and the reaction mixture was separated into an TABLE] Treating Gas I CO Alkylate yield, basis olefin consumed (wt.71)

Alkylate Composition (Vol.7!)

C, 2.3 3.6 C 4.8 5.6 C, 4.7 5.7 Cu 56.4 53.6 C 31.9 '.31.4 Alkylate Bromine No. 2.6 3.8 C, Distribution (Vol. 7!

- of Alkylate) Trimethyl pentane 43.1 36.9 Dimethyl hexane 3.0 3.6 Unidentified C 10.3 3.1

From the Table l itcan readily be seen that the alkylation reaction employing carbon dioxide treated sulfuric acid catalyst was more selective for production of desirable C range alkylate, and particularly for production of desirable trimethyl pentanes than was the alkylation reaction employing nitrogen treated sulfuric acid catalyst. Additionally, the bromine number, indicating degree of unsaturat ion, was lower for alkylate produced in the reaction using the carbon dioxide treated sulfuric acid catalyst.

EXAMPLE II In the same reactor system employed in Example I, additional alkylation reactions were performed to show the advantage of using the carbon dioxide treated sulfuric acid of the present invention, as compared to alkylation reactions using untreated sulfuric acid. Summaries of operating conditions and analytical results for these alkylation runs are shown in Table lI below.

TABLE 11 Run Number 1 2 3 4 5 6 7 Acid (M1) 100 100 100 100 100 100 100 H SO,(wt. '7: in acid) 94.6 96.13 96.13 96.1 94.6 96.13 94.6 CO treating pressure (psig) 600 75 80 85 CO wt. of Acid 0.3 0.6 0.8 0 0 0 Hydrocarbon Charge (gms) 78 72 78 75 78 76 76 lsobutane/butene-Z ratio 6.4/1 6.6/1 6.6/1 6.6/1 6.4/1 6.6/1 6.6/1 Alkylation temperature (F.) 47-50 50 50 50 50 50 Alkylation pressure (psig) 95 80 45 60 55 Alkylation reaction time (min) 15 15 l5 15 15 15 15 Alkylate recoveryv pent-ane and heavier (gms) 20.4 17.5 19.6 21.3 14.9 15.5 19.4 Alkylate yield (wt.7z olefin) 192 195 190 205 142 149 170 Alkylate composition (VF/1.7!)

C 2.1 2.5 2.5 2.0 1.4 2.7 3.0 C 4.3 5.0 5.0 4.8 3.3 5.6 5.6 C 4.3 4.9 4.8 4.9 4.0 5.8 5.5 Cg 72.3 61.9 62.6 60.4 60.6 63.1 59.0 C 17.0 25.6 25.1 27.9 30.7 22.6 26.7 Alkylate Bromine Number 1.7 3.0 3.4 4.2 5.4 3.0 4.6 C fraction composition (Vol.7;

of Alkylate) Trimethyl pentane 58.0 49.2 50.9 47.0 42.8 46.2 43.3 Dimethyl hexane 4.7 3.2 3.8 4.4 4.9 4.6 Unidentified C, 9.6 10.5 11.7 9.8 13.3 12.0 11.1

Runs 1 through 4 were made employing carbon dioxide treated sulfuric acid alkylation catalyst. ln run 1, sulfuric acid was mixed with carbon dioxide at 600 psig and 50F. for 48 hours. At the end ofthis time, pressure was reduced and the alkylation reaction was performed at psig. ln Runs 24, carbon dioxide was added to the sulfuric acid in the reaction vessel, in the weight fractions shown and the alkylation reactions were performed at the resulting pressures. For runs 57, no additive was employed with the sulfuric acid catalyst.

From an examination of the results obtained in this example, alkylation runs employing carbon dioxide treated sulfuric acid catalyst produce greater yields of alkylate, as a weight percent of olefin consumed in the reaction, than alkylation runs employing untreated acid catalyst. Also, the alkylate from the treated catalyst runs contains greater amounts of Chg hydrocarbons, particularly the desirable trimethyl pentane isomers. As indicated by the Bromine number, olefin content of alkylate produced with treated catalyst is lower than for alkylate produced with untreated catalyst.

From the foregoing discussion and examples, the advantages of the improvement of the present invention can readily be seen. By employing a carbon dioxide treated sulfuric acid alkylation catalyst in the alkylation of lower molecular weight isoparaffin hydrocarbons with olefins having three to five carbon atoms, alkylate of improved quality can readily be obtained.

Obviously, many modifications and variations of the an acid catalyst selected from the group consisting of sulfuric acid. fluorosulfonic acid, and mixtures thereof at a temperature in the range of about zero to about F and a superatmospheric pressure; the improvement'which comprises:

a. treating said acid catalyst with carbon dioxide to form an acid catalyst having a weight ratio of carbon dioxide to acid of at least 0. 1/100 at a temperature in the range of about zero to about 100F and a superatmospheric pressure in the range of from about 50 psig to about 1000 psig; and

b. alkylating said isoparaffin hydrocarbon with said alkylating agent in the presence the carbon dioxide treated acid catalyst of step (a).

2. The process of claim 1 wherein the treating step (a) temperature is in the range of about 20F to about 75F, the pressure is in the range of about 50 psig to about 1000 psig, and the acid catalyst is contacted with carbon dioxide in a weight ratio of carbon dioxide to acid in the range of about 0.3/100 to about 5/100.

3. The process of claim 2 wherein treated acid catalyst from step (a) contains from about 0.3 to about 0.8 weight percent carbon dioxide;

4. The process of claim 3 wherein isoparaffin reactant is isobutane and the alkylating agent is selected from the group consisting of propylene, butylenes, pentylenes and mixtures thereof.

5. The process of claim 4 wherein the acid catalyst is sulfuric acid. 

1. IN AN ALKYLATION PROCESS WHEREIN ISOPARAFFIN HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF ISOBUTANE, ISOPENTANE AND MIXTURES THEREOF IS ALKYLATED WITH AN ALKYLATING AGENT SELECTED FROM THE GROUP CONSISTING OF PROPYLENE, BUTYLENES, PENTYLENES, THEIR SULFATES, AND MIXTURES THEREOF IN THE LIQUID PHASE, IN THE PRESENCE OF AN ACID CATALYST SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID, FLUOROSULFONIC ACID, AND MIXTURES THEREOF AT A TEMPERATURE IN THE RANGE OF ABOUT ZERO TO ABOUT 100*F AND A SUPERATMOSPHERIC PRESSURE, THE IMPROVEMENT WHICH COMPRISES: A. TREATING SAID ACID CATALYST WITH CARBON DIOXIDE TO FORM AN ACID CATALYST HAVING A WEIGHT RATIO OF CARBON DIOXIDE TO ACID OF AT LEAST 0.1/100 AT A TEMPERATURE IN THE RANGE OF ABOUT ZERO TO ABOUT 100*F AND A SUPERATMOSPHERIC PRESSURE IN THE RANGE OF FROM ABOUT 50 PSIG TO ABOUT 1000 PSIG, AND B. ALKYLATING SAID ISOPARAFFIN HYDROCARBON WITH SAID ALKYLATING AGENT IN THE PRESENCE THE CARBON DIOXIDE TREATED ACID CATALYST OF STEP (A).
 2. The process of claim 1 wherein the treating step (a) temperature is in the range of about 20*F to about 75*F, the pressure is in the range of about 50 psig to about 1000 psig, and the acid catalyst is contacted with carbon dioxide in a weight ratio of carbon dioxide to acid in the range of about 0.3/100 to about 5/100.
 3. The process of claim 2 wherein treated acid catalyst from step (a) contains from about 0.3 to about 0.8 weight percent carbon dioxide.
 4. The process of claim 3 wherein isoparaffin reactant is isobutane and the alkylating agent is selected from the group consisting of propylene, butylenes, pentylenes and mixtures thereof.
 5. The process of claim 4 wherein the acid catalyst is sulfuric acid. 